This invention relates generally to assisting the natural heart in operation and, more specifically, to actuating a wall of the natural heart.
The natural human heart and accompanying circulatory system are critical components of the human body and systematically provide the needed nutrients and oxygen for the body. As such, the proper operation of the circulatory system, and particularly, the proper operation of the heart, are critical in the overall health and well-being of a person. A physical ailment or condition which compromises the normal and healthy operation of the heart can therefore be particularly critical and may result in a condition which must be medically remedied.
Specifically, the natural heart, or rather the cardiac tissue of the heart, can fail for various reasons to a point where the heart can no longer provide sufficient circulation of blood for the body so that life can be maintained. To address the problem of a failing natural heart, solutions are offered to provide ways in which circulation of blood might be maintained.
Some solutions involve replacing the heart. Other solutions are directed to maintaining operation of the existing heart. One such solution has been to replace the existing natural heart in a patient with an artificial heart or a ventricular assist device. In using artificial hearts and/or assist devices, a particular problem stems from the fact that the materials used for the interior lining of the chambers of an artificial heart are in direct contact with the circulating blood. Such contact may enhance undesirable clotting of the blood, may cause a build-up of calcium, or may otherwise inhibit the blood""s normal function. As a result, thromboembolism and hemolysis may occur. Additionally, the lining of an artificial heart or a ventricular assist device can crack, which inhibits performance, even when the crack is at a microscopic level. Moreover, these devices must be powered by a power source which may be cumbersome and/or external to the body. Such drawbacks have limited use of artificial heart devices to applications having too brief of a time period to provide a real lasting benefit to the patient.
An alternative procedure also involves replacement of the heart and includes a transplant of a heart from another human or animal into the patient. The transplant procedure requires removing an existing organ (i.e. the natural heart) from the patient for substitution with another organ (i.e. another natural heart) from another human, or potentially, from an animal. Before replacing an existing organ with another, the substitute organ must be xe2x80x9cmatchedxe2x80x9d to the recipient, which can be, at best, difficult, time consuming, and expensive to accomplish. Furthermore, even if the transplanted organ matches the recipient, a risk exists that the recipient""s body will still reject the transplanted organ and attack it as a foreign object. Moreover, the number of potential donor hearts is far less than the number of patients in need of a natural heart transplant. Although use of animal hearts would lessen the problem of having fewer donors than recipients, there is an enhanced concern with respect to the rejection of the animal heart.
In an effort to continue use of the existing natural heart of a patient, other attempts have been made to wrap skeletal muscle tissue around the natural heart to use as an auxiliary contraction mechanism so that the heart may pump. As currently used, skeletal muscle cannot alone typically provide sufficient and sustained pumping power for maintaining circulation of blood through the circulatory system of the body. This is especially true for those patients with severe heart failure.
Another system developed for use with an existing heart for sustaining the circulatory function and pumping action of the heart, is an external bypass system, such as a cardiopulmonary (heart-lung) machine. Typically, bypass systems of this type are complex and large, and, as such, are limited to short term use, such as in an operating room during surgery, or when maintaining the circulation of a patient while awaiting receipt of a transplant heart. The size and complexity effectively prohibit use of bypass systems as a long term solution, as they are rarely portable devices. Furthermore, long term use of a heart-lung machine can damage the blood cells and blood borne products, resulting in post surgical complications such as bleeding, thromboembolism function, and increased risk of infection.
Still another solution for maintaining the existing natural heart as the pumping device involves enveloping a substantial portion of the natural heart, such as the entire left and right ventricles, with a pumping device for rhythmic compression. That is, the exterior wall surfaces of the heart are contacted and the heart walls are compressed to change the volume of the heart and thereby pump blood out of the chambers. Although somewhat effective as a short term treatment, the pumping device has not been suitable for long term use. Typically, with such compression devices, a vacuum pressure is needed to overcome cardiac tissue/wall stiffness, so that the heart chambers can return to their original volume and refill with blood. This xe2x80x9cactive fillingxe2x80x9d of the chambers with blood limits the ability of the pumping device to respond to the need for adjustments in the blood volume pumped through the natural heart, and can adversely affect the circulation of blood to the coronary arteries. Furthermore, natural heart valves between the chambers of the heart and leaching into and out of the heart are quite sensitive to wall and annular distortion. The movement patterns that reduce a chamber""s volume and distort the heart walls may not necessarily facilitate valve closure (which can lead to valve leakage).
Therefore, mechanical pumping of the heart, such as through mechanical compression of the ventricles, must address these issues and concerns in order to establish the efficacy of long term mechanical or mechanically assisted pumping. Specifically, the ventricles must rapidly and passively refill at low physiologic pressures, and the valve functions must be physiologically adequate. The myocardial blood flow of the heart also must not be impaired by the mechanical device. Still further, the left and right ventricle pressure independence must be maintained within the heart.
Another major obstacle with long term use of such pumping devices is the deleterious effect of forceful contact of different parts of the living internal heart surface (endocardium), one against another, due to lack of precise control of wall actuation. In certain cases, this coaptation of endocardium tissue is probably necessary for a device that encompasses both ventricles to produce independent output pressures from the left and right ventricles. However, it can compromise the integrity of the living endothelium.
Mechanical ventricular wall actuation has shown promise, despite the issues noted above. As such, devices have been invented for mechanically assisting the pumping function of the heart, and specifically for externally actuating a heart wall, such as a ventricular wall, to assist in such pumping functions.
Specifically, U.S. Pat. No. 5,957,977, from which priority is claimed and which is incorporated herein by reference in its entirety, discloses an actuation device for the natural heart utilizing internal and external support structures. That patent provides an internal and external framework mounted internally and externally with respect to the natural heart, and an actuator or activator mounted to the framework for providing cyclical forces to deform one or more walls of the heart, such as the left ventricular wall. The present invention further adds to the art of U.S. Pat. No. 5,957,977 and specifically sets forth various embodiments of activators or actuator devices which are suitable fordeforming the heart walls and supplementing and/or providing the pumping function for the natural heart.
Accordingly, it is an objective of the present invention to provide a device and method for actively assisting the natural human heart in its operation.
It is still another objective of the present invention to actuate and assist the heart at a proper natural rate in a way suitable for long term usage.
It is another objective of the present invention to assist the heart while allowing one or more of the heart chambers to rapidly and passively refill at low pressure after the actuating device has completed an actuation stroke.
It is a further objective of the present invention to do so while providing different independent pressures on the left and right side of the natural heart.
It is a still further objective of the invention to assist the heart in a way which minimizes damage to the coronary circulation and the lining tissue or endocardium of the heart.
It is another objective of the present invention to assist the heart while maintaining the competence of the heart valves in their natural function.
These objectives and other objectives and advantages of the present invention will be set forth and will become more apparent in the description of the invention below.
The present invention addresses the above objectives and other objectives, and provides an actuation system for assisting the operation of the natural heart. The actuation system comprises a framework for interfacing with the natural heart. The framework includes one or more internal framework elements which are configured to be positioned within the interior volume of a heart. The framework further includes one or more external framework elements which are configured to be proximate an exterior surface of the heart. The internal and external framework elements are coupled together to form a structure which cooperates with the heart. In one embodiment, the external framework elements are coupled proximate the chamber of the heart and along the wall or walls of that chamber or chambers which are to be actuated in accordance with the principles of the present invention.
An actuator system is coupled to the framework and is configured to engage an exterior surface of the heart. For example, if the left ventricle of the heart is to be actuated utilizing the invention, the external framework element will be positioned proximate to the left ventricle exterior wall, and then the actuator system will be similarly positioned. The actuator system comprises an actuator band extending along a portion of the heart wall exterior surface. The actuator band is selectively movable between an actuated state and a relaxed state, and is operable, when in the actuated state, to assume a predetermined shape or curvature, and thereby indent a portion of the heart wall to effect a reduction in the volume of the heart, and specifically a reduction in one of the chambers of the heart, for assisting the heart in its pumping function.
In one embodiment of the invention, the actuator band includes a plurality of juxtaposed elements, such as blocks, which are coupled together by one or more actuator cords. The blocks are configured to be drawn together when the actuator band is in the actuated state, and to cooperate with each other, when drawn together, to assume the predetermined shape or curvature. The one or more cords which couple the blocks together are coupled to a drive apparatus to be moved by that apparatus and draw the blocks together to achieve such predetermined shape. The blocks have adjacent cooperating surfaces which are at least partially coextensive with each other when the blocks are drawn together in the actuated state. The actuator band is coupled or fixed at one or both of its ends to the external framework element and the drive apparatus is operable for selectively moving the actuator band between the relaxed and actuated states to achieve the desired assistance of the natural heart. In accordance with another aspect of the present invention, one or more curvature limiting devices, such as curvature limiting bands, are coupled to the actuator band. The curvature limiting bands limit the predetermined shape or curvature that may be imposed by the actuator band, on the heart surface-at the actuator band edges, at the yoke edges, or elsewhere, when it is in the actuated state in order to reduce the severity of the indentation against the actuated portion of the heart wall. In that way, the heart wall is shaped, and the volume of the heart is changed in a less severe manner which will limit the stress on the heart wall and heart. Preferably, the curvature limiting bands are operable for limiting the curvature imposed on any part of the external heart wall to a certain measurable degree of the natural relaxed and distended curvature of the heart wall, along which the actuator band extends. When the actuator band is in the relaxed state, it is operable to generally assume the natural curve of the distended, relaxed heart wall and does not offer resistance to the refilling of the heart, such that active filling of the heart chambers may be avoided.
In another aspect of the present invention, a paving surface might be positioned between the epicardium, or exterior surface of the heart, and the actuator band in order to provide smoother actuation and less damage to the epicardium.
In another embodiment of the invention, multiple actuator bands are utilized in combination with multiple curvature limiting bands, for actuating the heart at several positions along an exterior wall surface.
The drive apparatus of the invention is positioned remotely from the framework, heart and actuator band, and is coupled to the band through one or more cords which couple the elements or blocks together. In that way, the actuator band may be actuated remotely from the heart. One such drive apparatus utilizes a solenoid which is coupled to the one or more cords and selectively moves those cords to selectively move the actuator band between the actuated and relaxed states. Preferably, an energy storing device, such as a spring or elastic element is coupled between the armature or plunger of the solenoid and the cords. In that way, upon movement of the solenoid, the actuator band is moved more gradually to the actuated state from the relaxed state to further reduce the immediate stress to the heart wall and heart. The remote drive apparatus may be surgically positioned in the body at a site which is readily accessible, and particularly more accessible than the chest cavity and the heart. In that way, the drive system may be adapted, repaired, or upgraded, without the invasiveness of cardiothoracic surgery. The drive system will include one or more energy-providing elements for operating the solenoid or other drive elements of the apparatus. Further details of the invention are set forth hereinbelow in the drawings and detailed description.